A novel method and a sand/water remediation system with a photocatalytic fuel cell

ABSTRACT

The present invention belongs to the sewage treatment and sand remediation technology, it is about a new type of system and method about sand/water remediation with photocatalytic fuel cell. The characteristic photocatalytic fuel cell (PFC) using photons or solar energy to produce highly active electron/holes is introduced into soil remediation system to degrade pollutants. In the constructed Visible light photocatalytic fuel cell sand water remediation system, there was overlying water above polluted sands in a tubular reactor. Allowing static adsorption equilibrium to buildup, in the built photocatalytic fuel cell, the photocatalytic anode and photoelectric catalytic cathode were connected by wires with an external resistance. Using 50 W halogen lamp as the light source, it maintains photocatalysis and electrocatalytic reactions to degrade pollutants in the system. By degrading the pollutants in the overlying water, the pollutants in the sand were also desorbed and degraded, and rapidly decreased to a very low level. Thus in this system water purification treatment and sand remediation take place simultaneously.

TECHNICAL FIELD

The present invention belongs to the sewage treatment and soil/sand remediation technology, involving the preparation of catalytic electrode, building integrated synergetic photocatalysis and electrocatalysis in photocatalytic fuel cell sand/water restoration system. The system could introduce and generate active species that degrade pollutants and generate electricity simultaneously, decontaminate sand/water and recover energy .

BACKGROUND

Photocatalytic fuel cell (PFC) is a new kind of fuel cell, in which Photocatalytic cathode and photocatalytic anode electrodes are connected by wire with external resistance. When photocatalytic electrodes are illuminated by photons that have higher energy than the band gap, they produce abundant active electron/holes, which then form active oxidizing species degrade pollutants efficiently. The electrons transfer from the anode to the catalytic cathode through the external circuit timely, promote separation of electronic/holes on the electrodes. They can achieve electricity recovery and pollutants removal at the same time. PFCs with catalytic electrodes overcome the shortcoming of powder catalysts and greatly improve the Photocatalytic degradation efficiency of pollutants, in the meantime generate electricity.

Environmental pollution and energy consumption are two major challenges to the whole world, soil/sands are important parts in ecological environment, may have been polluted in varied degrees, soil pollution could directly lead to changes in the composition and physical/chemical properties of the soil, damage the normal function, decrease agricultural production and cause serious economic loss. Soil remediation technologies mainly are physical, chemical or biological methods, that transform, being adsorbed/absorbed and/or degraded, that reduce the concentration of the pollutants in soil, and convert to harmless components to environment or human. New Soil remediation techniques are still being developed, many are in early stage, followed developments in equipments for engineering application are started at a relatively even late stage . Facing increasingly serious soil pollution, it is of great significance to develop sustainable technologies to restore/remediate contaminated sites.

Photocatalytic fuel cell, can use clean solar energy , produce electricity at the same time, promote the degradation of pollutants, it has great value as a novelty fuel cell system. The existing soil remediation methods have their own specific application scope and limitation. No reports were found about introducing photocatalytic fuel cells to soil remediation. This application introduces photocatalytic fuel cell into soil remediation system, with polluted sand as pollution medium, the constructed Special photocatalytic fuel cells for sand/water remediation are demonstrated and proved. By increasing the degradation rate of pollutants and producing electricity, the application is expected providing an efficient, low-cost, eco-environmental-friendly method of soil/sand remediation.

Contents

The purpose of the invention is to provide a new kind of sand/water remediation system, thus visible light photocatalytic fuel cell was constructed with Ag/Ag/GO as anode catalyst and ZnIn₂S₄ as cathode photocatalyst, plus that the introduction of reactive species such as manganese (III) from KMnO4/bisulfite promoted photoelectrocatalytic degradation of pollutants, achieved remediation of water/sand sites finally using visible lights illumination.

Technical scheme of the invention:

A new type photocatalytic fuel cell was used to decontaminate polluted sites with sand/water, Steps are as follows:

Based on the features of photocatalytic fuel cell, which can produce highly active electronic/holes to degrade pollutants under solar illumination, PFC was introduced into soil remediation/decontamination system, by constructing visible light/solar light photocatalytic fuel cell in sand/water remediation system.

The system consisted of in tubular reactor with overlying water and sand, where static adsorption equilibrium might establish. The photocatalytic fuel cell was built containing photocatalytic anode and photoelectric catalytic cathode connected by wires with 50 W halogen lamp as the light source, that photocatalysts and electrocatalytic reaction were carried out to degrade pollutants. By degrading the pollutants of the overlying water, the pollutants in sand was decreased, the content of pollutants in the sand was reduced to a very low level, achieved the remediation function.

Active species were produced by dropping in KMnO₄ bisulfite, MnO₄ ⁻ reacted with HSO₃ ³¹ formed Mn(III), thus improved photocatalytic degradation of pollutants.

Cyclodextrin was added to the system, it promotes the mass transfer between sand and water, that more pollutants migrated from the sand to the overlying water, and then degraded by photoelectrocatalysis, achieved water purification and sand remediation.

The photocatalytic anode is Ag/Ag/GO and the photocatalytic cathode is ZnIn₂S₄. Ag/Ag/GO nanophotocatalyst was prepared by precipitation-photo reduction method, using silver ammonia solution as the silver source, and it was used as anode catalyst.

ZnIn₂S₄ was synthesized by hydrothermal method and ZnIn₂S₄ was used as cathode photocatalyst.

Silica sol was prepared by stirring the mixture, which made by ethyl orthosilicate, anhydrous ethanol, deionized water and Concentrated hydrochloric acid at a volume ratio of 4.5:10:9:2.45. Adding catalysts into silica sol, stirred throughly to a gain a homogeneous paste. Catalytic electrodes were prepared by evenly coated the paste into stainless steel mesh with the size 5 cm*3 cm, then dried at room temperature. The amount of nanophotocatalyst per square centimeter is 5 mg.

The benefits of the invention are as follows: The present invention provides a new method for the decontamination and degradation of pollutants in polluted sites with sand/water. Using photocatalytic fuel cells produce highly active electron/holes under solar illumination, so pollutants were degraded by photocatalysis and electrocatalysis. Photocatalytic fuel cell in sand remediation system, with active Mn(III) introduced, simultaneously accelerate the degradation of pollutants and produced electricity; In addition, through promoting the mass transfer of pollutants between sand and water interface from the sand to the overlying water using CD, the pollutants in the sand decreased more quickly with the degradation of overlying water. The system achieved purification of sand/water, which provided an efficient and low-cost, ecological and environmental soil restoration method.

DESCRIPTION OF FIGURES

FIG. 1 is a comparison diagram of the degradation effect of the pollutants in the overlying water before and after the addition of sodium bisulfite/potassium permanganate in the process of sand/water remediation in photocatalytic fuel cells.

FIG. 2 shows the decontamination of sand pollution in the remediation system of sodium bisulfite/potassium permanganate. The concentration of pollutants in the sand was obviously reduced.

FIG. 3 is a comparison diagram of the degradation effect of the pollutants in the overlying water after cyclodextrin was added to the remediation system.

FIG. 4 shows the distribution of pollutants in water and sand over time in the remediation system.

IMPLEMENTATION CASES

The following are detailed descriptions of the implementation example of the technical scheme and the attached figures.

Implementation 1: The Degradation of Tetracycline in the Sand/Water Remediation System of Photocatalytic Fuel Cell

At the bottom of the tubular reactor, 25 g of sand was added, and 150 mL of 20 mg/L tetracycline solution was put into the reactor, settled 1 d for adsorption equilibrium. Catalyst Ag/AgCl/GO loaded stainless steel was used as Photocatalytic anode, ZnIn2S4 loaded on stainless steel as photocatalytic cathode, an external 51Ω resistance was connected, with 50 w halogen lamp placed on the top, the light source was 5 cm from the solution surface. Take samples at intervals for analysis. If Add KMnO₄ and NaHSO₃ at the same time (The concentration of KMnO4 in the solution was 7 mg/L, and NaHSO₃ was 23 mg/L), then water samples and soil samples were taken simultaneously for analysis measurement. The water samples were measured by uv-visible spectrophotometer at 358 nm after filtration of 0.45 um. The soil samples were dried in 50° C. in oven. 3 mL extract was added with the mixture of 0.1 mol/L NaCl, 0.5 mol/L oxalate and ethanol (25/25/50 volume ratio). After fully shaking, followed ultrasound treatment for 15 min, 8000 r/min centrifugation for 10 min. Repeat the above extraction for three times, the extract was determined after filtration.

FIG. 1 shows that as time goes on, the degradation rate of tetracycline in the solution was increasing, more significantly after the addition of KMnO₄and NaHSO₃. FIG. 2 shows that the content change of tetracycline in sand before and after the addition of KMnO₄ and NaHSO₃. The results showed that the content of tetracycline in the sand was significantly decreased after the addition.

Implementation 2: The Effect of Cyclodextrin on the Degradation of Tetracycline in the Remediation System

25 g of sand was added to the bottom of the tubular reactor, 150 ml 20 mg/L, tetracycline solution was put in, also 5 mg cyclodextrins. The tetracycline solution without cyclodextrin was used as the control group, set aside for one day stay for adsorption equilibrium; With 50 w halogen lamp placed above the reactor, catalyst Ag/AgCl/GO was loaded stainless steel for Photocatalytic anode, stainless steel as cathode 51Ω external resistance was connected in the circuit, water samples were took at intervals, measured by uv-visible spectrophotometer after filtration of 0.45 um.

FIG. 3 shows that the content of tetracycline in solution decreases gradually, the degradation rate increases with time. After adding cyclodextrin, the degradation rate of tetracycline is increased.

Implementation 3: The Degradation of RhB in the Sand/Water Remediation System of Photocatalytic Fuel Cell

25 g of sand was added to the tubular reactor, 150 mL 20 mg/L RhB solution with 0.1 mol/L Na₂SO₄ was put in. It was set aside for one day, after reaching adsorption equilibrium. Photocatalytic fuel cells was constructed using electrodes inserted in overlying water (using Ag/AgCl/GO loaded photocatalytic anode and ZnIn₂S₄ loaded cathode), 100Ω external resistance was connected. 50 w halogen lamps were installed on both sides of the catalytic electrodes for vertical illumination, 5 cm away from photocatalytic electrodes. Water samples and soil samples were took at intervals, The water samples were filtered by 0.45 um filter and measured at 553 nm with spectrophotometer. The sand was extracted using ultra pure water. 3 mL water extract was added for extraction each time, then vortex, ultrasonic treatment 15 min, then 8000 r/min centrifugation for 10 min, repeated extraction three times. All extracts were combined after three extractions, then the extract was measured.

FIG. 4 shows the concentration of RhB in overlying water and sand. The concentration of RhB in sand/water gradually decreased over time. It shows that the concentration of RhB in overlying water can influence the distribution of RhB in sand. By degrading and decreasing the content of RhB in the overlying water, the content in sand was also reduced and the remediation was achieved. 

1. A novel system and method of sand/water remediation with photocatalytic fuel cell, wherein: in characteristic photocatalytic fuel cells, photons and/or solar energy are used to excite highly active electron/holes to degrade pollutants; thus, a soil/sand remediation system made of visible light responsive photocatalytic fuel cell was constructed to decontaminate solid sands from pollutions; the system consisted of overlying water above sand in a tubular reactor; the pollutant solution that may reach static adsorption equilibrium was treated; the photocatalytic fuel cell has built-in immersed photocatalytic anode and photoelectric catalytic cathode that are connected by wires; and 50 W halogen lamp was used to simulate the solar light, it maintains photocatalysis and electrocatalytic reaction that degrade pollutants inside the system; by degrading the pollutants in the overlying water, the pollutants in sand was also desorbed and degraded, that decreased the content in sand to a very low level, thus achieved the remediation purpose.
 2. The novel system according to the sand/water remediation system described in claim 1, wherein when Mn(III) was produced by dropping-in solution containing KMnO₄ /bisulfate, MnO₄ ⁻ reacted with HSO₃ ⁻ and that introduced new active species, that improved photocatalytic degradation of pollutants.
 3. The novel system according according to claim 1 about sand/water remediation system and method, wherein cyclodextrin was added to the sand, promoting the mass transfer between sand and water, more pollutants migrated from sand to the overlying water, then being degraded by photoelectrocatalysis, achieved water decontamination and sand remediation.
 4. The novel system according to the sand/water remediation system of claim 1, the system and method wherein the anode photocatalyst is Ag/Ag/GO and the cathode photocatalyst is ZnIn₂S₄.
 5. The novel system according to the sand/water remediation system of the claim 3, wherein the photocatalytic anode has Ag/Ag/GO and the photocatalytic cathode has ZnIn₂S₄.
 6. The novel system according to the sand/water remediation system mentioned in the claim 4, wherein the anode Ag/Ag/GO catalyst was prepared by precipitation-light reduction method, in which silver-ammonia solution was used as a silver source; the cathode photocatalyst ZnIn₂S₄ was synthesized by a hydrothermal method; silica sol was prepared by stirring the mixture of ethyl orthosilicate, anhydrous ethanol, deionized water and concentrated hydrochloric acid, at a volume ratio of 4.5:10:9:2.45; after-adding photocatalysts into the silica sol, the sol was stirred throughly to a gain a uniform sol-paste; catalytic electrodes were prepared by evenly coating the sol-paste onto a stainless steel mesh eg sized at 5 cm*3 cm, then dried at room temperature; the amount of nanophotocatalyst per square centimeter is 5 mg.
 7. The novel system according to the sand/water remediation system of claim 5, wherein the anode Ag/Ag/GO catalyst was obtained by precipitation-light reduction method, in which silver-ammonia solution was used as a silver source; the photocatalytic cathode ZnIn₂S₄ was synthesized by hydrothermal method; silica sol was prepared by stirring a mixture with ethyl orthosilicate, anhydrous ethanol, deionized water and concentrated hydrochloric acid at a volume ratio of 4.5:10:9:2.45; after adding catalysts into silica sol, the sol was stirred throughly to a gain a homogeneous sol paste; catalytic electrodes were prepared by evenly coating the paste into stainless steel mesh eg with the size of 5 cm*3 cm, then air dried at room temperature; the amount of nanophotocatalyst per square centimeter is 5 mg. 